Circulation of the cerebrospinal fluid (=CSF). The intra- and the extracerebral CSF spaces are marked by a blue color. The arrows mark the normal CSF circulation from the site of main production (chorioid plexus of the ventricles) to the main sites of absorption (sagittal sinus and spinal vessels). According to new studies, a substantial amount of CSF leaves the skull by the perineural sheets and enters the lymphatic vessels of the neck.